It is C-day plus one and a time to reflect and regret, not least because this year's UK census may be the last. Did you count the rooms in your home correctly? Are you sure, even now, how many people live there? Did you complete the optional answer on religion? How do you get to work? Are you sure you remembered to post it?

If you didn't, you have until 6 May to return the form online, just so long as you can imagine yourself back to 27 March. Even then, no one seems to be exactly racing ahead with the count. When computers can deliver an election result within a matter of hours, you have to ask why it will take more than a year for the Office for National Statistics to come up with the total population figure, and still longer to crunch the rest of the numbers. Don't marketing people manage something similar in a matter of days? Maybe that is why it's their information that governments may decide to rely on in future.

Before it's quite gone, though, let's appreciate the census for one thing: as a reminder of how few civic responsibilities in this country are truly compulsory. We don't have to vote, or possess a passport or – now they've been abolished in advance – an ID card. But if you don't return your census form, you risk a fine of £1,000 and a criminal record.